The last time I saw my 14-year-old nephew, he showed me his phone. He was playing a game that pitted World War II-era tanks against one another, and he wanted me to see his impressive digital inventory of U.S. model Shermans, Pattons and Lees.

Then he entered the game’s in-app store, where “premium” tanks are sold for real money. He scrolled to the one he really wanted: An American T34. I stared incredulously at the price: $52.89.

Upgrades for games are nothing new. Teenagers (and many adults, for that matter) have been plunking down cash ingames like World of Warcraft for years, even before the iPhone made its debut. But in-app purchases have succeeded in making anything and everything an upgrade. With all manner of digital currencies are available, and our kids are faced with more opportunities to buy than ever.

In recent weeks, plenty of stories have emerged about what can happen when adults don’t make the call. A 7-year-old charged $5,900 buying dinosaurs in the game “Jurrasic World,” Yahoo Tech reported. A teenager playing a soccer game on Xbox charged $7,600 for different groups of players (and apparently sold his dad a story that he didn’t know what was happening). A couple of kids who unblocked a family data cap racked up $1,700 in overage fees. Yikes.

Those stories are clearly extreme examples, and a recent study reported that the average iPhone user spent an average of $35 on apps in 2015, primarily for games. But how would you feel if you saw an unauthorized $20 charge for Donut Dollars to speed up construction of the Duff Beer factory in The Simpsons iOS game? Get this: You can buy 2,400 donuts for only $99.99.

Right. Here’s how to make sure you’re the one who approves all in-app purchases on your child’s iPhone or iPad.

If your child has his or her own device:

Turn on restrictions to disable in-app purchases.

Open the Settings app

Tap “General”

Tap “Restrictions”

Tap “Enable Restrictions”

Choose a password that’s different from your iPhone’s unlock PIN

Now, you’ll be able to turn off in-app purchases completely by flipping the switch from green to white

J.R. is a reporter, editor, designer and former news desk leader with footprints in newsrooms in the Deep South and Northeast. He is the director of marketing communications for FamilySignal and writes from Birmingham, Alabama.